On the behavioural relevance of optional and mandatory impure public goods : results from a laboratory experiment

Ethical goods are increasingly available in markets for conventional goods giving proethically motivated consumers a convenient option to contribute to public goods. In a previous experiment we explored the behavioural relevance of impure public goods in a withinsubject setting and observed reduced aggregate prosocial behavior in the presence of impure goods that favor private consumption at the expense of public good provision. In this experiment, we implement a between]subject design to test the behavioural relevance of impure public goods with only a token contribution to a public good cause. From a theoretical perspective, assuming people demand private and public characteristics regardless of how they are provided, we would expect no behavioural relevance of the presence of impure public goods. However, this experiment establishes that prosocial behaviour defined as contributing to a public good, is negatively affected by impure goods with token contributions, in comparison to when they are absent. Furthermore, if the token impure good is mandatory instead of optional the negative effect on pro]social behaviour seems to be offset. The results from this experiment suggest impure public goods are not behaviourally irrelevant, can decrease pro]social behaviour but their optional or mandatory nature can have different behavioural consequences.